Miraculously escaping a direct-to-download release, P. Rex easily elicits expectations that it'll be pretty much ignored at the multiplex, but there’s always a slim chance that, Sharknado-like, it could provoke a cult-fan frenzy. Not likely in this case, however, particularly since ITN distribution has reduced the initial weeklong run to a single weekend.

At least the movie’s tropical scenery provides intermittent distraction. While diving illegally to recover a trove of Spanish gold coins from a shipwreck near the coast of Belize to pay off debts owed to local gangster Tariq (Gildon Roland), mercenary treasure hunter Jax (Brian Krause) and his crew are attacked by a massive, unknown underwater predator after setting off explosive charges in the vicinity of the wreck. Jax is the only survivor, recovered unconscious from his shattered dive boat by daytrip operator Henry (Berne Velasquez), who is leading tourist couple Rod (Steven Helmkamp) and Jane (Candice Nunes) on a snorkeling outing.

Based on Jax’s partial account of the attack, which withholds crucial details about the deadly creature and the gold treasure, Henry calls on the help of marine biologist Sarah (Anne McDaniels), who insists on diving into the deepwater “blue hole” where Jax’s encounter occurred. At the bottom, they find an accumulation of large eggs and, after taking one back to her lab, Sarah and Jax crack open the shell, releasing a small, nasty, green-skinned, dinosaur-like critter that immediately goes on the attack, conveniently shredding through a group of Tariq’s thugs, who arrive at the lab in pursuit of Jax.

Dubbing the undiscovered species “Poseidon Rex,” Sarah realizes now that the little predator’s parent that has emerged from underwater hibernation can’t be far off — a suspicion that’s confirmed when the towering monster chows down on a boat full of partygoers, then rampages onshore to destroy the beachside resort. Sarah, Jax and Rod flee to a nearby abandoned military base, where they’ll have to devise a plan to warn the rest of the world about the newfound threat menacing humanity and try to save their own skins at the same time.

At least director Mark L. Lester, who wrangled 2005’s somewhat similarly themed Pterodactyl (and has a remarkably long list of familiar-sounding credits), has some dinosaur-monster movie cred going for him, but he faces an uphill challenge with the resources available for this pic. Aside from the insertion of poorly matched stock footage of scenes involving scuba divers and military jets (but no combat helicopters as depicted in the movie poster), which the project obviously couldn’t afford to stage itself, the biggest issue is clearly with the CGI dinosaurs. Although mildly menacing in appearance, with massive T Rex-like jaws and teeth, both the overall anatomy and movement of the creatures, not to mention their amphibian adaptations, are just too implausible to seem remotely threatening.

The often inane screenplay, by frequent Lester collaborator Rafael Jordan (Dragons of Camelot, Pterodactyl), vaguely recognizable cast struggling to make the script seem intelligible and strictly functional cinematography betray the movie’s most earnest intentions, however. Lacking sufficient self-parody to entertain as a campy monster-movie spoof or the budget to thrill as action-adventure or sci-fi, much like the creature it depicts, Poseidon Rex represents a throwback that even its own distributor can't really get behind.